This invention relates generally to sound systems for use in meeting rooms such as government council chambers and corporate board rooms. More specifically, this invention is directed to such a sound system in which multiple signal sources such as microphones and multiple loudspeakers are employed to facilitate voice pickup and distribution throughout the meeting room. Typically, such a system utilizes a microphone at every seat as well as at a podium or lecturn and a loudspeaker proximate every microphone location as well as at various other locations within the meeting room. Without adjusting the audio level of a loudspeaker or group of loudspeakers located proximate to a particular microphone that is being used, audio feedback occurs that produces an undesirable and disruptive squeal in the audio system. It is therefore desirable and, hence, is a principal object of the present invention to provide a sound system in which the audio level of each loudspeaker or group of loudspeakers located proximate to a microphone in use is automatically proportionately attenuated to prevent unwanted audio feedback in the sound system and to provide a comfortable audio level for those listeners seated near the person speaking into that microphone.
This and other objects of the present invention are accomplished by providing a sound system that employs control logic to effect low level switching of the audio signal to selectively attenuate the audio output of a given loudspeaker or group of loudspeakers as a function of the source of that audio signal. By employing low level switching in accordance with the teachings of the present invention, improved efficiency is achieved by avoiding the use of high power loss elements such as relays, power resistors, and transformers. In addition, the sound system of the present invention has the advantages of silent switching, low power requirements, lower construction cost, and improved reliability.